Performance of the FASTNET Narrowband VHF
Frequency Hopping Tactical Radio in
Challenging Multipath Environments
Adrien Le Naour, Francois Pipon, Benny Nahoum, Dominique Merel, Bernhard Obrist
Abstract— FASTNET is the latest tactical VHF radio from THALES. It offers multiple waveforms in frequency hopping,
including a new (time multiplex based) waveform called GEOMUX. Multipath situations had been identified and synchronization
multipath related changes had been designed for the previous radio generation for Switzerland. Realistic propagation channels are
required for the development and testing of a robust communication systems. Thus, Channel sounding in the 30-88 MHz band has
been performed in Switzerland (in Jura and the Alps) and has confirmed the existence of challenging multipath propagation with
delay spread up to 80 s. This results in a dual problem : Inter Symbol Interference (ISI) up to 3 modulated symbols in 25 kHz
channel bandwidth and potential problems in hop synchronization strategy. In this article, a highly sensitive multipath detection
channel sounder is first introduced. Then, an analysis of the measured channel impulse responses is provided. A method to extract
propagation parameters from previous measurements is also described. A realistic and reproducible channel model has been
developed and injected into a waveform test environment. FASTNET signal processing has been successfully tested on this test
environment. The results were confirmed with dedicated field trials in Switzerland, both for the legacy Combat Net Radio (CNR)
mode and the multi-services GEOMUX modes. It shows significant range improvements due to the equalization and
synchronization design.
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